In modern times of advanced technological development, liquid crystal displays (LCDs) have been widely applied to electronic display products such as TVs. computer screens, notebook computers, mobile phones, or personal digital assistants (PDAs). An LCD includes data drivers, scan drivers, and an LCD panel. The LCD panel has a pixel array. The scan divers are used for turning on multiple pixel rows in the pixel array sequentially for scanning the pixel data output by the data driver to pixels and thus displaying the image.
A general scan driver comprises a decoding circuit and a plurality of level-shift drivers. The decoding circuit outputs a decoding signal to the plurality of level-shift drivers according to a decoding control signal. The plurality of level-shift drivers produces scan signal sequentially according to the decoding signal for scanning the display panel. In other words, the driving method of the LCD panel is to use a gate as the control for turning on the internal unit. Then a source supplies the accurate voltage for controlling the orientation of liquid crystals in the display panel. Because the output voltage of the gate includes a high voltage (VGH) and a low reference voltage (VGL), high-voltage devices has to be adopted. The scan driving circuit thereof has to raise the scan signal to the high voltage (VGH) and the low reference voltage (VGL) by means of the level-shift drivers. Thereby, the circuit area is larger.
FIG. 1 shows a circuit diagram of a level-shift driver according to the prior art. As shown in the figure, the level-shift driver according to the prior art comprises a first level-shift unit 10′, a second level-shift unit 20′, and an output driving unit 30′. The first level-shift unit 10′ is used for receiving and shifting the level of the decoding signal G1 and transmitting the shifted decoding signal to the second level-shift unit 20′. The level-shifted decoding signal G1 by the first level-shift unit 10′ is shifted again. Then, the second level-shift unit 20′ transmits the twice-shifted decoding signal G1 to the output driving unit 30′. According to the twice-shifted decoding signal G1, the output driving unit 30′ produces the scan signal for scanning the display panel.
Nonetheless, according to the prior art, three levels of level-shift drivers are used for shifting the level of the scan signal. Thereby, at least ten high-voltage transistors and two resistors should be used for completing a set of level-shift drivers. Consequently, the area of the scan driving circuit according to the prior art is increased, and so does the cost.
Accordingly, the present invention provides a novel scan driving circuit, which uses a control circuit for reducing the circuit area of each level-shift driving circuit and thus reducing the cost. The problem described above can be thereby solved.